Conventionally, a gate of a transistor such as an IGBT or the like is driven by a gate drive circuit, which typically drives the gate of the transistor by a constant electric current drive. In such configuration, it may be preferable to set up a power supply voltage for a current regulator circuit that supplies the constant electric current to have a certain voltage value, in order to satisfy an operating range of the current regulator circuit for the supply of the constant current toward the gate of the IGBT. Therefore, a gate voltage at a time of an ON operation of the IGBT performed in a saturation region (i.e., at a time of Full-ON) may become higher than required. If the gate voltage is too high and exceeds a gate dielectric breakdown voltage VGEs of the IGBT, a problem may arise, such as a deterioration of the reliability of a gate oxide film, a shortened life of the IGBT, and the like.
On the other hand, the disclosure in a patent document 1 (i.e., Japanese Patent Laid-Open No. 2009-011049) describes a gate driver, which is configured to perform a constant electric current drive of the gate of the IGBT by a current regulator circuit at a turn-ON start time and is configured to switch to perform a constant voltage drive by a constant voltage drive circuit at a certain timing before the Full-ON of the IGBT. In this case, a voltage of a dedicated power supply VDD2 of a current regulator circuit is set up to be higher than a voltage of a dedicated power supply VDD1 of a constant voltage drive circuit. Therefore, the gate voltage at the time of Full-ON is restricted, while the operating range of the current regulator circuit is being secured.
However, in the gate driver in the disclosure of the patent document 1, two drive circuits (i.e., a current regulator circuit and a constant voltage drive circuit) and two power supplies (i.e., a dedicated power supply VDD1 and a dedicated power supply VDD2) are required. Therefore, a circuit configuration is complicated in such a gate driver. Further, the manufacturing cost of such a driver is high.